JPH06284763A - Speed controller for servomotor - Google Patents

Abstract

PURPOSE:To obtain constant dynamic characteristics even when load inertia is changed by providing a load inertia estimating means, comparing the actual value of load inertia and the value of load inertia currently set to a torque observer and updating the currently set value of load inertia. CONSTITUTION:An inertia estimating equipment 30 is composed of an inertia estimation start-end signal generator 30a, a load-torque estimate feature detecting means 30b and an inertia set-value changing means 30c. The inertia estimation start-end signal generator 30a generates an inertia estimation start signal by the alteration of a speed command value wmr. The load-torque estimate feature detecting means 30b monitors the variation of load torque tauLp estimated by a torque observer, and detects and outputs the sign (positive or negative) of the maximum deviation. The inertia set-value changing means 30c changes an inertia set value in the inverse transfer function 20 of a mechanical system by the sign.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control device for a servo motor used as an actuator for NC processing machines and robots.

[0002]

2. Description of the Related Art Conventionally, a servomotor used as an actuator for an NC processing machine, a robot or the like is usually subjected to speed control in order to keep its speed constant.

In speed control using feedback control, a torque observer is added to the speed control system in order to obtain a desired response regardless of fluctuations in load torque.

The torque observer is a device for estimating the torque of the load by using the output torque of the motor calculated by the control device and the acceleration of the driven object from the sensor.
By adding the output of this torque observer to the output of the speed control, it is possible to cancel the influence of the load torque and keep the response of the speed control constant within a certain range.

A block diagram of speed control using such a torque observer is shown in FIG. As shown in FIG. 4, the deviation between the speed command value ωmr and the actual speed ωm of the servomotor is supplied to the speed control unit 50.
The speed control unit 50 outputs the current command icr by PI control based on the deviation, similarly to the speed control described above. The sum of this current command icr and the load torque value ilr calculated by the torque observer 58, which will be described later, is calculated and supplied to the servo motor. The transfer function of the current of the servo motor is represented by the transfer function 52, and the sum of the above currents ir (= ic
r + ilr) is converted by the transfer function 52 into a current i that actually flows in the servo motor. The torque τm actually generated in the servomotor by the current i is a value obtained by multiplying the current i by the torque constant 54. The value obtained by subtracting the load torque τL from this τm is added to the mechanical system to determine the actual speed of the servomotor. That is, the actual servomotor speed ωm can be obtained by applying the mechanical transfer function 56 to the effective torque τe.

The torque observer 58 estimates the load torque from the servo motor current i and the servo motor speed ωm. First, the torque constant set value 5 for the servo motor current i
The estimated value τmp of the servo motor torque τm is calculated by applying 8a. On the other hand, servo motor speed ωm
Then, the inverse transfer function 58b of the mechanical system is applied to calculate τep, which is the estimated value of the effective torque τe. The inverse transfer function 58b is the inverse transfer function of the mechanical system transfer function 56. The estimated value τLp of the load torque is calculated by subtracting τep from τmp thus obtained.

Since the torque observer 58 is usually composed of a digital signal processor or the like, a delay of the sampling period occurs. In FIG. 5, the delay of the sampling period is represented by the first-order delay element 58c. Note that, as shown in FIG. 5, τLp thus obtained is converted into a corresponding current value by the reciprocal 60 of the set value of the torque constant. That is, the load torque current ilr is calculated by converting the load torque into a current,
As described above, the sum of the load torque current ilr and the current command icr is supplied to the transfer function 52 of the servo motor.

In this way, it is possible to eliminate the influence of the load torque τL. Therefore, in terms of equalization, FIG.
The same speed control as the simple speed control block as shown in FIG.

FIG. 5 is a block diagram of speed control by classical PI control. As shown in FIG. 5, the deviation between the speed command value ωmr from the upper controller and the actual speed ωm of the motor is input to the speed control unit 70. The speed control unit 70 outputs the current command icr by PI control based on this deviation. This current command icr is converted into the actual current i of the servo motor by the transfer function 72 of the servo motor. The torque actually generated in the servomotor by the current i is a value obtained by multiplying the current i by the torque constant 74. The actual speed is obtained by applying this actual torque to the mechanical system of the load. That is, the actual torque is converted to the actual speed ωm by the transfer function 76 of the mechanical system. This speed ωm is detected by the speed sensor and used to calculate the deviation from the speed command value ωmr described above.

As can be seen from FIG. 5, the response characteristic of the controlled object in this case is uniquely determined by the speed control gain K and the load inertia set value Jn.

[0011]

The conventional servo motor controller is constructed as described above, and the influence of the load torque can be eliminated. However, in reality, the inertia of the load may fluctuate greatly. For example, the NC processing machine has to process the workpieces having various inertias, and the inertias of the assembly objects handled by the robot also vary. In this way, when the actual load inertia J changes with respect to the set value Jn of the load inertia in the torque observer,
A large change appears in the dynamic characteristics. This is shown in FIG. FIG. 6 is a graph showing changes in the poles of the transfer function, where the horizontal axis is the real axis and the vertical axis is the imaginary axis. As shown in FIG. 6, when the actual load inertia J becomes about 5 times or more the set value Jn, the dynamic characteristics change greatly.

Therefore, conventionally, there has been a problem that the dynamic characteristics of the load inertia change greatly due to the change of the load inertia.

The present invention has been made to solve the above problems, and an object thereof is to obtain a servomotor control device that achieves a constant dynamic characteristic even if the load inertia changes.

[0014]

In order to solve the above-mentioned problems, the present invention uses the current applied to the servo motor, the rotation speed of the servo motor, and a preset load inertia value to determine the above-mentioned values. In a servomotor control device that performs speed control of the servomotor using a torque observer that estimates a load torque of a control target connected to the servomotor, the load torque output by the torque observer is monitored, and the servo The two load torque values of a steady load torque that is a load torque value when the rotation speed of the motor is constant, and an acceleration load torque that is a load torque value when the rotation speed of the servo motor is changing. Is the actual load inertia value larger than the load inertia value currently set for the torque observer from the difference between Load inertia estimation means for determining whether or not the torque observer sets the present value if the actual load inertia value is determined to be greater than the presently set load inertia value by the load inertia estimation means. If the actual load inertia value is determined to be less than the currently set load inertia value, then the currently set load inertia value is increased. A speed control device for a servo motor, characterized in that the value of the load inertia set at present is updated by decreasing it by a predetermined value.

[0015]

The load inertia estimating means according to the present invention calculates the difference between the steady load torque and the acceleration load torque, and from the difference, the actual load inertia value and the load inertia value currently set in the torque observer. And to determine which is greater. Then, if the actual load inertia is larger, the set load inertia value is increased by a predetermined amount, and if not, it is decreased. By repeating this process, the load inertia set in the torque observer becomes equal to the actual load inertia.

[0016]

EXAMPLE First, the principle of estimating the load inertia will be described. As shown in FIG. 4, which is a configuration block diagram of a conventional control device, the load torque τL is expressed by the following equation. [tau] L = Kti-Js [omega] m-D [omega] m (1) Here, D is a resistance component proportional to speed, and generally viscous resistance corresponds to this. Further, the torque observer 58 shown in FIG. 4 is a minimum dimension observer using the so-called Gopinath method, and as shown in FIG. 4, its estimated load torque τLp is expressed by the following equation. . τLp = (1 / (1 + sT)) (Ktni−Jnsωm−Dnωm) (2) where Ktn is a set value of the torque constant in the torque observer, and Dn is a set of viscous resistance in the torque observer. It is a value. In addition, T represents the delay time of the observer, as described above. Specifically, it represents the sampling period of the torque observer data.

Since it can be considered that the torque constant does not change during control, Kt = Ktn. Further, since it can be considered that the viscous resistance does not change, D = Dn. Above (1) (2)
The following equation is obtained from the equation. τLp = (1 / (1 + sT)) (τL + (J−Jn) sωm) (3) This (3) is the actual torque τL and the estimated value τL.
It shows the relationship with p. As understood from the equation (3), a non-zero error dJ (= J−Jn) between the inertia set value Jn and the actual inertia value J.
If dωm / dt ≠ 0, the torque proportional to the error dJ is added to the estimated value and output from the torque observer.

The estimated value during steady operation is τLpave. Further, an estimated value that maximizes the deviation of the estimated value τLp output from the torque observer from τLpave when the speed changes is τLpmax. Then, by the sign of the deviation (τLpmax−τLpave) between them,
The magnitude relationship between the inertia set value and the actual value is recognized.

For example, when dτLp> 0, J> J
It is judged as n, the current set value Jn is increased, and dτ
If Lp <0, J <Jn is determined and the current set value Jn is decreased. It is possible to set J = Jn by repeating such an operation while dτLp ≠ 0.

A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a servo motor control device according to this embodiment. As shown in FIG. 1, what is characteristic of this embodiment is that an inertia estimator 30 is newly provided, and other configurations are the same as the conventional speed control device shown in FIG. Is the same as
That is, the deviation between the speed command value ωmr and the actual speed ωm is supplied to the speed control unit 10, and the speed control unit 10 outputs a current command. The sum of this current command and the load torque value is converted by the transfer function 12 into the actual current generated in the servo motor. By multiplying this current by the torque constant 14, the torque generated in the servo motor can be obtained. Then, a torque obtained by subtracting the load torque τL from the generated torque is applied to the mechanical system, and as a result (by the transfer function 16 of the mechanical system), the actual speed ωm of the servo motor is determined.

The torque observer has a torque constant set value of 1
8. The reverse transfer function 20 of the mechanical system and the first-order lag element 22 are provided, and the respective operations are the same as those of the conventional speed control device.

The inertia estimator 30 having a characteristic structure in this embodiment is composed of an inertia estimation start / end signal generator 30a, a load torque estimated value feature detecting means 30b and an inertia set value changing means 30c. The inertia estimation start / end signal generator 30a determines the speed command value ω
mr is monitored, and a start signal for estimation of inertia is generated according to a change in the speed command value ωmr (for example, 1000 rpm to 2000 rpm). The load torque estimated value feature detection means 30b is a detection means that monitors the change in the load torque τLp estimated by the torque observer and outputs the sign (positive or negative) of the maximum deviation. The inertia set value changing means 30 changes the inertia set value in the inverse transfer function 20 of the mechanical system using this code.

The detailed operation of this embodiment will be described below with reference to the flow chart. FIG. 2 shows a first flowchart showing the operation of this embodiment.

In FIG. 2, first, the average value of the estimated load torque value τLp output by the torque observer in a steady state is calculated. Therefore, in step S2-1, the loop variable N for counting the number of times of averaging is initialized to "0".

In step S2-2, it is determined whether N is an odd number or an even number. If N is an even number, the process proceeds to step S2-3.
If it is an odd number, the process proceeds to step S2-4.

In step S2-3, in order to detect the torque observer output at a position that is an even multiple of the angle .phi.c of the cogging cycle of the servo motor, it waits until the rotational position of the servo motor reaches a predetermined position. On the other hand, step S2-
In No. 4, in order to detect the observer output at a position that is an odd multiple of the angle φc of the cogging cycle, it waits for the rotational position of the servo motor to reach a predetermined position. The reason why the torque is obtained at each of the odd-numbered position and the even-numbered position is to eliminate the cogging noise in the AC servomotor.

The speed command is changed in step S2-5, and the output of the torque observer is stored in step S2-6. This storage is performed in the load torque estimated value feature detector 30b.

In step S2-7, the speed command is restored.

In step S2-8, it is checked whether the loop variable N is N0. If it is N0, it is considered that the data sufficient for obtaining the average value in the steady operation are gathered, and the process proceeds to step S2-10. Otherwise, the process proceeds to step S2-9.

At step S2-9, N is incremented, the routine proceeds to step S2-2, and the above-mentioned processing is repeated.

In step S2-10, the average value is calculated based on the data obtained as described above. By this, the average value of the load torque τLp output by the torque observer during steady operation is obtained.
This average value is called τLpave.

Next, when the inertia estimation start / end signal generator 30a detects that the speed command value ωmr has changed, the load torque estimated value feature detecting means 30b samples the estimated load torque value τLp output by the torque observer. ,Remember. Then, if a fixed number of sampling values are obtained in step S3-1 of FIG.
Among them, the largest deviation from the steady value is obtained. This is called τLpmax.

Next, in step S3-3, the deviation between the maximum value τLpmax and the steady value τLpave is calculated. That is, dτLp = τLpmax−τL
Calculate pave.

In this embodiment, the deviation between the largest deviation from the steady value and the steady value is obtained in this way. This is to obtain the largest possible deviation and reduce the error. Generally, in a mechanical control device, it is necessary to use a measured value having a large absolute value of the measured value because noise such as cogging noise of an AC servo motor and nonlinear viscosity is large.

In step S3-4, it is checked whether dτLp is "0". As a result, dτLp
If = 0, the process proceeds to step S3-5, and the inertia set value in the torque observer is not changed. On the other hand, if dτLp ≠ 0, the process proceeds to step S3-6, and it is checked whether dτLp is positive or negative. If it is determined in step S3-6 that dτLp is positive, the process proceeds to step S3-7, and if it is determined that dτLp is negative, the process proceeds to step S3-8. In step S3-7, the set value Jn of inertia in the torque observer is decreased by a predetermined step amount.

In step S3-8, the set value Jn of inertia in the torque observer is increased by a predetermined step amount.

By performing the above processing, the set value of the inertia in the torque observer is updated. In the present embodiment, the inertia set value is updated by a predetermined number of steps depending on whether the value of dτLp is positive or negative. Therefore, by repeating the above process several times, dτLp = 0
It is possible to The speed control device for the servomotor in this embodiment is composed of a digital signal processor and its program. That is, the torque observer and the inertia estimator are realized by the routines of the corresponding programs.

As described above, according to this embodiment, the estimated value τL of the load torque output from the torque observer.
The load inertia can be estimated by detecting the change in p from the steady value. Therefore, the set value of the load inertia set in the torque observer is updated based on the change in the load. Therefore, even if the inertia of the load driven by the servo motor changes, the dynamic characteristics of the control system can be kept constant.

[0040]

As described above, according to the present invention, the value of the actual load inertia is estimated, the value is compared with the value currently set in the torque observer, and the load is determined based on the comparison result. Since the set value of the inertia is increased or decreased by a predetermined value, the load torque is estimated based on the actual load inertia value, so that a servo motor control device that can make the dynamic characteristics constant more accurately can be obtained. Has the effect. Further, according to the present invention, since the load inertia is always updated by a predetermined value, it has an effect of being strong against noise from the outside. Further, since the update calculation is easy, there is an effect that it can be easily implemented by a digital signal processor, a microprocessor, or the like.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a servo motor control device that is a preferred embodiment of the present invention.

FIG. 2 is a first flowchart showing the operation of the servo motor control device shown in FIG.

FIG. 3 is a second flowchart showing the operation of the servo motor control device shown in FIG. 1.

FIG. 4 is a configuration block diagram of a conventional servo motor control device.

5 is a block diagram of an equalizing structure in the servo motor control device shown in FIG. 4 when the load torque is constant.

6 is a graph showing changes in poles of a transfer function with respect to changes in load inertia in the controller for the servo motor shown in FIG.

[Explanation of symbols]

 10 speed control unit 12 transfer function 14 torque constant 16 mechanical transfer function 18 torque constant set value 20 reverse transfer function of mechanical system 22 first-order lag element 30 inertia estimator 30a inertia estimation start / end signal generator 30b load torque estimated value feature Detecting means 30c Inertia set value changing means

Front page continuation (72) Inventor Nobuyuki Matsui Gokisho-cho, Showa-ku, Nagoya, Aichi Prefecture (no street number) Inside Nagoya Institute of Technology

Claims (1)

[Claims] 1. A load torque of a control target connected to the servo motor is estimated from a current applied to the servo motor, a rotation speed of the servo motor, and a preset load inertia value. In a servomotor control device that performs speed control of the servomotor using a torque observer, the load torque output by the torque observer is monitored,
The two loads, a steady load torque that is a load torque value when the rotation speed of the servo motor is constant, and an acceleration load torque that is a load torque value when the rotation speed of the servo motor changes. Load inertia estimation means for determining whether or not the actual load inertia value is greater than the load inertia value currently set in the torque observer from the difference between the torque values, and the torque observer includes the load inertia. If the estimation means determines that the actual load inertia value is larger than the currently set load inertia value, the currently set load inertia value is increased by a predetermined value, and the actual load inertia value is increased. If it is determined that the value is less than the load inertia value currently set, the load inertia currently set A speed control device for a servo motor, wherein the currently set load inertia value is updated by decreasing the inertia value by a predetermined value.